In U.S. Pat. No. 4,093,533, which is incorporated herein by reference, it is taught that chrysotile asbestos fibers are relatively easily bonded together with polymeric fluorocarbons, but that crocidolite asbestos fibers are not readily bonded together with polymeric fluoro-carbons to form strong diaphragms for use in chlor-alkali electrolytic cells (see, e.g., Col. 2, lines 62-67 of the patent).
It has now been found that polymeric fluorocarbons can be made to readily bond crocidolite asbestos fibers into a strong diaphragm for use in chloralkali electrolytic cells by lowering the pH (to about 2 or lower) of the aqueous slurry which contains the particulate polymer and asbestos fibers, then proceding with the diaphragm formation.